Fix: Managers that incorrectly derive from SchedulerDependentManager

Change conductor and network managers to be ordinary managers. Also
remove some unnecessary imports from managers already declared with
base manager classes in nova/manager.py.

Resolves bug 1154070.

Change-Id: I6b87cd5d7d5ef66425d084db667a6eff247cf0b1
Merge "Fix: Managers that incorrectly derive from SchedulerDependentManager"